(1) Field of the Invention
The present invention relates to a high-intensity discharge lamp and high-pressure mercury lamp that are used in general lighting fixtures and optical instruments, and also relates to an illumination device using the high-pressure mercury lamp and an image display apparatus using the illumination device.
(2) Description of Prior Art
Conventionally, in an illumination device used in an image display apparatus such as a liquid crystal projector, a light source and a concave reflecting mirror are usually formed in one piece. As the light source, a high-pressure mercury lamp with a short arc, which is close to a point light source, has been used. The high-pressure mercury lamp has advantages, such as an excellent luminous efficiency, high intensity, favorable balance of red, blue, and green in emitted light, and long lifetime.
Such a high-pressure mercury lamp is provided with a glass tube with sealing parts set at its both ends, the glass tube including a pair of electrodes. Inside a discharge space of the glass tube, mercury used as light-emitting material and argon gas for starting-up are sealed under a predetermined pressure.
Using this conventional high-pressure mercury lamp, however, there has been a problem that it takes a long time for light flux to attain 90% of its stable state after the lamp is started up (this period of time is referred to as the xe2x80x9clight buildup timexe2x80x9d hereinafter). This is because only mercury is sealed as the light-emitting material.
This problem is explained more specifically as follows. In the high-pressure mercury lamp, a temperature of the central point of arc discharge increases to about 6,000 K or higher after the lamp is started up. At this high temperature, atoms of mercury are excited to emit lights. Mercury is in a liquid state at room temperature, and so it takes long for mercury to be vaporized as the temperature of the inner wall surface of the glass tube increases through discharge. This unavoidably leads to a longer light buildup time.
Especially in the case of a high power lamp that is relatively large in the shape of a glass tube, the light buildup time would be very long, such as approximately 5 to 10 minutes.
Although the conventional high-pressure mercury lamp provides high intensity, it has a problem about the light buildup time as described above. In particular, when the high-pressure mercury lamp is used in an image display apparatus, such as a liquid crystal projector, it takes too long before images are displayed.
It should be noted here that the stated problem associated with the light buildup time generally occurs to high-intensity discharge lamps that use material aside from mercury as the light-emitting material.
It is therefore an object of the present invention to provide a high-intensity discharge lamp and a high-pressure mercury lamp that each have an improved light buildup time.
The object of the present invention can be achieved by a high-pressure mercury lamp made up of: an arc tube which includes a discharge space, mercury and xenon gas being sealed in the discharge space; and a pair of electrodes which are set facing each other in the discharge space of the arc tube.
With this construction, xenon gas emits light immediately after the lamp is started up, thereby considerably improving the light buildup time.
It is preferable that the amount of mercury per unit volume that is to be sealed in the discharge space is within a range of 0.12 mg/mm3 to 0.35 mg/mm3. Also, the pressure of the xenon gas in the discharge space is preferably within a range of 2.0xc3x97105 Pa to 2.0xc3x97106 Pa.
At least one of chlorine, bromine, and iodine is sealed as a halogen substance into the discharge space of the arc tube. Thus, by means of the halogen cycle, occurrence of blackening on the inner wall of the arc tube can be reduced, so that the life of the lamp is increased.
It is preferable that the total amount of the halogen substance per unit of volume that is to be sealed in the discharge space is within a range of 1.0xc3x9710xe2x88x927 xcexcmol/mm3 to 1.0xc3x9710xe2x88x922 xcexcmol/mm3.
The object of the present invention can be also achieved by a high-intensity discharge lamp made up of: an arc tube which includes a discharge space, at least a part of a wall of the arc tube being transparent and two kinds of light emitting materials which are respectively in a liquid state and a vapor state at a room temperature being sealed in the discharge space; and a pair of electrodes, each of which passes through the wall of the arc tube and is inserted into the discharge space.
With this construction, the light emitting material in a vapor state first emits light immediately after the lamp is started up, and then the light emitting material in a liquid state is gradually vaporized to emit light as a temperature in the discharge space of the arc tube rises. Consequently, the light buildup time can be considerably reduced as compared with a case where only a light emitting material in a liquid state is sealed in the arc tube.
The object of the present invention can be also achieved by a high-intensity discharge lamp made up of: an arc tube which includes a discharge space, at least a part of a wall of the arc tube being transparent and a first light emitting material and a second light emitting material whose light buildup time is shorter than the first light emitting material being sealed in the discharge space; and a pair of electrodes, each of which passes through the wall of the arc tube and is inserted into the discharge space.
With this construction, the second light emitting material with a shorter light buildup time emits light immediately after the lamp is started up, and the first light emitting material gradually emits light. Here, as the first light emitting material, it is preferred to use a material having an excellent luminous efficiency and an advantage contributing to an increase in the life of the lamp. Since the second light emitting material is sealed in addition to the first light emitting material, the light buildup time can be reduced as compared with a case where only the first light emitting material is used. At the same time, the excellent high-intensity discharge lamp taking full advantage of the first light emitting material can be realized.